SF6 Breakdown in Cylindrical Field with dc Voltage.

Investigations were made in a coaxial cylinder system at high dc-voltages up to 900 kV and at high gas pressures up to 6 bar. The SF//6-breakdown-behavior can be classified into three regions according to the following aspects: I) breakdown after steady corona discharges, II) validity of the similarity law for the discharge onset voltage, III) deviations of the similarity law with a marked polarity effect. Possible explanations are given for the polarity effect and the deviations in region III. The results can be of importance for a future application of SF//6-insulation in HVDC systems.